Tag Archives: carabid beetles

Unless you have lived in a news vacuum for the last two weeks or so, you will be aware of the impending “Ecological Armageddon” that is about to be unleashed upon us. A paper in the journal PLoS ONE in which it was reported that there had been a 75% decline in the biomass of flying insects in protected areas in Germany since 1989 was the starting pistol that began the media frenzy. The newspapers, both broadsheet and tabloids were quick to react as were the radio and TV stations and the coverage was global as this selection of links shows.

Entomologists were in great demand for a few days, all being asked to comment gravely on the paper and its implications. I was also persuaded to air my thoughts on air, Talk Radio having caught me at an unguarded moment. I should never have answered the ‘phone 😊

As the media frenzy subsided, the more considered responses began to appear. Manu Saunders very sensibly attempted to put the study in perspective and point out its limitations. Two entomologists from the Game & Wildlife Conservancy Trust which hold an even longer data set, put forward their interpretation and an ecological consultancy also took the opportunity to comment. The authors of the paper and the blog commentators were careful not to point the finger directly at pesticides as the main cause of this decline, although they did rule out climate change. Agricultural intensification and the practices associated with it, were however, suggested as likely to be involved in some way, something that has been known for more than a century as the naturalist and novelist Gene Stratton-Porter pointed out in 1909 in her novel A Girl of the Limberlost,

“Men all around were clearing available land. The trees fell wherever corn would grow. The swamp was broken by several gravel roads…Wherever the trees fell the moisture dried, the creeks ceased to flow, the river ran low, and at times the bed was dry. From coming in with two or three dozen rare moths a day, in three years time Elnora had grown to be delighted with finding two or three. Big pursy caterpillars could not be picked from their favourite bushes, where there were no bushes. Dragonflies could not hover over dry places and butterflies became scare in proportion to the flowers”.

What puzzles me about the media response is why now and why this particular study? We have known for a long time that some insect groups have been in decline for many years. The parlous state of UK butterflies and moths has been highlighted on more than one occasion over the last couple of decades (e.g. Conrad et al., 2004; Thomas et al., 2004; Fox et al., 2013), and declines in the abundance of bibionid flies (D’Arcy-Burt & Blackshaw, 1987), dragonflies (Clausnitzer et al., 2009) and carabid beetles (Brooks et al., 2012) have also been noticed and written about. In addition, the results of a 42-year study on insects associated with cereal fields in SE England was published recently (Ewald et al., 2015), with little or no fanfare associated with it. I commented on the decline of some insect species (and entomologists) in a blog post in 2013 and in December of last year, wrote about the general decline of insect numbers and lack of long term studies, incidentally citing the German study when it was originally published in a little known German publication back in 2013 and with far fewer authors 😊

The media response to this not new news puts me in mind of the Ash Die Back scare of 2012 when the press and politicians having

Pests and diseases recorded as entering the UK 1960-2015. The two arrows indicate the replacement of local forest offices with central district offices and reduction in entomology and pathology staff.

been warned and made aware of the increasing incidence of non-native pests and pathogens entering the country for many years beforehand, suddenly, and in response to an intractable problem, went overboard in reporting doom and destruction

My hypothesis, for what it is worth, is that it is like when a tap washer starts to wear out, and your tap starts to drip. At first you just ignore it or turn the tap ever more tightly every time you use it. Eventually something gives, either the tap breaks off (this happened to me very recently) or the drip becomes a flood. Either way, something needs to be done, i.e. call the plumber. In the case of the Ash Die Back episode, the UK government responded positively, albeit too late to prevent it, but by setting up the Tree Health and Plant Biosecurity Expert Taskforce of which I was privileged to be a member, recommendations were made that resulted in increased forest research funding and additional legislation being put in force to hopefully reduce the chances of further invasions. I suspect that the current “Ecological Armageddon” scenario will not result in a similar response, although it may encourage research councils worldwide to think more seriously about funding more research into sustainable agriculture and for governments to encourage farmers to adopt farming strategies that encourage more wildlife and use fewer inputs. At the same time, given the increasing number of studies that implicate urbanisation as a major factor in the decline of insect numbers (e.g. Jones & Leather, 2012; Dennis et al., 2017) it would behove local planning authorities to increase their efforts to provide much-needed green spaces in our towns and cities and to ban the use of decking in gardens and the replacement of front gardens with concrete and tarmac car parking areas.

What it does highlight as Manu Saunders said in her blog, is that we need funding for more long-term studies. We also need to find instances where the data already exist but have not yet been analysed, amateur records and citizen science projects may be of use here. Alternatively, as was very recently done in France (Alignier, 2018), it is possible, using the identical protocol, to resample a site after a gap of decades, to see what changes have occurred.

I hope for the sake of our descendants that the reports of an “Ecological Armageddon” have been exaggerated. This should however, be a wake-up call to all those with the power to do something to mitigate the decline in biodiversity worldwide. Governments need to respond quickly and to think long-term and responsibly. The current attitude of politicians to adopt a short-term ‘how safe is my job’ political viewpoint is no longer a viable one for the planet. It is precisely that attitude that got us into the situation that we find ourselves in now.

I have been musing about extinctions and shifting baselines for a while now; BREXIT and an article by Simon Barnes in the Sunday Times magazine (3rd September 2016) finally prompted me to actually put fingers to keyboard. I fear that BREXIT will result in even more environmental damage than our successive governments have caused already. They have done a pretty good job of ignoring environmental issues and scientific advice (badgers) even when ‘hindered’ by what they have considered restrictive European legislation and now that we head into BREXIT with a government not renowned for its care for the environment I become increasing fearful for the environment. Remember who it was who restructured English Nature into the now fairly toothless Natural England, because they didn’t like the advice they were being given and whose government was it who, rather than keep beaches up to Blue Flag standard decided to reclassify long-established resort beaches as not officially designated swimming beaches? And, just to add this list of atrocities against the environment, we now see our precious ‘green belt’ being attacked.

My generation is liable to wax lyrical about the clouds of butterflies that surrounded us as we played very non PC cowboys and Indians outside with our friends in the glorious sunshine. We can also fondly reminisce about the hordes of moths that used to commit suicide in the lamp fittings or beat fruitlessly against the sitting room windows at night. The emptying of the lamp bowl was a weekly ceremony in our house. We also remember, less fondly, having to earn our pocket-money by cleaning our father’s cars, laboriously scraping the smeared bodies of small flies from windscreens, headlamps and radiator grilles on a Saturday morning. A few years later as students, those of us lucky enough to own a car, remember the hard to wash away red smears left by the eyes of countless Bibionid (St Mark’s) flies, as they crashed into our windscreens.

Are these memories real or are we looking back at the past through those rose-tinted glasses that only show the sunny days when we lounged on grassy banks listening to In the Summertime and blank out the days we were confined to the sitting room table playing board games?

We have reliable and robust long-term data sets showing the declines of butterflies and moths over the last half-century or so (Thomas, 2005; Fox, 2013) and stories about this worrying trend attract a lot of media attention. On a less scientific note, I certainly do not find myself sweeping up piles of dead moths from around bedside lamps or extricating them from the many spider webs that decorate our house. Other charismatic groups, such as the dragonflies and damselflies are also in decline (Clausnitzer et al., 2009) as are the ubiquitous, and equally charismatic ground beetles (carabids) (Brooks et al., 2012). But what about other insects, are they too on the way out? A remarkable 42-year data set looking at the invertebrates found in cereal fields in southern England (Ewald et al., 2015) found that of the 26 invertebrate taxa studied less than half showed a decrease in abundance; e.g. spiders, Braconid parasitic wasps, carabid beetles, Tachyporus beetles, Enicmus (scavenger beetles), Cryptophagid fungus beetles, leaf mining flies (Agromyzids), Drosophila, Lonchopteridae (pointed wing flies), and surprisingly, or perhaps not, aphids. The others showed no consistent patterns although bugs, excluding aphids, increased over the study period. Cereal fields are of course not a natural habitat and are intensely managed, with various pesticides being applied, so are perhaps not likely to be the most biodiverse or representative habitats to be found in the UK.

But what about the car-smearing insects, the flies, aphids and other flying insects? Have they declined as dramatically? My first thought was that I certainly don’t ‘collect’ as many insects on my car as I used to, but is there any concrete evidence to support the idea of a decline in their abundance. After all, there has been a big change in the shape of cars since the 1970s.

Top row – cars from 1970, including the classic Morris 1000 Traveller that my Dad owned and I had to wash on Saturdays.

Bottom row the cars of today, sleek rounded and all looking the same.

Cars were much more angular then, than they are now, so perhaps the aerodynamics of today’s cars filter the insects away from the windscreen to safety? But how do you test that? Then I remembered that the RSPB had once run a survey to address this very point. Sure enough I found it on the internet, the Big Bug Count 2004, organised by the RSPB. I was very surprised to find that it happened more than a decade ago, I hadn’t thought it was that long ago, but that is what age does to you 🙂

The “Splatometer” as designed by the RSPB

The idea, which was quite cool, was to get standardised counts of insect impacts on car number plates. The results were thought to be very low as the quote below shows, but on what evidence was this based?

“Using a cardboard counting-grid dubbed the “splatometer”, they recorded 324,814 “splats”, an average of only one squashed insect every five miles. In the summers of 30-odd years ago, car bonnets and windscreens would quickly become encrusted with tiny bodies.” “Many people were astonished by how few insects they splatted,” the survey’s co-ordinator Richard Bashford, said.

Unfortunately despite the wide reporting in the press at the time, the RSPB did not repeat the exercise. A great shame, as their Big Garden Birdwatch is very successful and gathers useful data. So what scientific evidence do we have for a decline in these less charismatic insects? Almost a hundred years ago, Bibionid flies were regarded as a major pest (Morris, 1921) and forty years ago it was possible to catch almost 70 000 adults in a four week period from one field in southern England (Darcy-Burt & Blackshaw, 1987). Both these observations suggest that in the past Bibionids were very common. It is still possible to pluck adult Bibionids out of the air (they are very slow, clumsy fliers) in Spring, but if asked I would definitely say that they are not as common as they were when I was a student. But as Deming once said, “Without data, you’re just another person with an opinion.” In the UK we are fortunate that a long-term source of insect data exists, courtesy of Rothamsted Research, the longest running agricultural research station in the world. Data have been collected from a nationwide network of suction and light traps for more than 50 years (Storkey et al., 2016). Most of the publications arising from the survey have tended to focus on aphids (Bell et al., 2015) and moths (Conrad et al., 2004), although the traps, do of course, catch many other types of insect (Knowler et al., 2016). Fortuitously, since I was interested in the Bibionids I came across a paper that dealt with them, and other insects likely to make an impact on cars and splatometers (Shortall et al., 2009). The only downside of their paper was that they only looked at data from four of the Rothamsted Suction Traps, all from the southern part of the UK, which was a little disappointing.

Location and results of the suction traps analysed by Shortall et al. (2009).

Only three of the trap showed downward trends in insect biomass over the 30 years (1973-2002) analysed of which only the Hereford trap showed a significant decline. So we are really none the wiser; the two studies that focus on a wider range of insect groups (Shortall et al., 2009; Ewald et al., 2015) do not give us a clear indication of insect decline. On the other hand, both studies are limited in their geographic coverage; we do not know how representative the results are of the whole country.

What a shame the RSPB stopped collecting ‘splatometer’ data, we would now have a half-decent time series on which to back-up or contradict our memories of those buzzing summers of the past.

Post script

After posting this I came across this paper based on Canadian research which shows that many pollinators, possibly billions are killed by vehicles every year. This reduction in insect numbers and biomass has also been reported in Germany.

I would be amazed if there are any entomologists who have not deployed a pitfall trap or two at some stage in their career. I would also hazard a guess that quite a few non-entomological ecologists have come across the joys of pitfall trap setting and catch sorting as part of their undergraduate training; most field courses seem to include a pitfall trap day, and rightly so. Pitfall trapping is after all, probably the simplest and most efficient way of collecting data, and not always insects 😉

Tapir pitfall trap

More seriously though, pitfall traps are a remarkably simple and incredibly versatile way of sampling insects, particularly those that are active on the soil surface (epigeal) e.g carabid beetles. They can be used in most habitats where you are able to dig into the soil,

are very cheap as they can be made from easily obtainable household materials and can be modified easily depending on your objectives and sampling conditions. It is very important however, that the lip of the trap is either flush with or below the soil surface. Not very many beetles or other invertebrates, are willing to climb up the steep sides to allow you to capture them. They are also amenable to being deployed in a variety of statistically meaningful ways. (Figure ‘borrowed’ from Woodcock (2005)). They are of course not perfect. Some of my students complain that they catch too much!

There has been, and continues to be, much debate about what the catch actually represents. Are they a measure of activity or of density, i.e. do the trap catches represent the most active and careless beetles, rather than the most abundant? Southwood (1966) in the first edition of Ecological Methods is fairly dismissive of their use except as a way of studying the activity, seasonal incidence and dispersion of single species and considered them to be of no use whatsoever in comparing communities. Other authors argue however, that if the trapping is carried out over a long period of time then the data collected can be representative of actual abundance (e.g. Gist & Crossley, 1973; Baars, 1979) and despite Southwood’s comments, they are probably most often used to compare communities (e.g. Rich et al., 2013; Zmihorski et al., 2013; Wang et al., 2014) For a very thorough account of the use and abuse of pitfall traps see Ben Woodcock’s excellent 2005 article (and I am not just saying that because he is one of my former students). You might expect, given the fact that pitfalls were used by our remote ancestors to trap their vertebrate prey, that entomologists would have adopted this method of trapping very early on, especially given the fact that nature got there first, e.g. as used by larvae of the antlion.

Antlion ‘pitfall traps’.

I was therefore surprised when I started researching this article to find that the earliest reference I could find in the scientific literature was Barber (1931). I found this very hard to believe so resorted to Twitter. Richard Jones suggested that a sentence in

Notes on Collecting and Preserving Natural History Objects

referring to silver sand pits might be a reference to an early form of pitfall trap. On further research however, it turned out that sand pits were the results of sand mining operations and were used opportunistically by entomologists. They worked in a very similar way to

But, I digress. My next port of call was The Insect Hunter’s Companion (Greene, 1880) which I felt certain would mention pitfall traps. To my surprise, in the 1880s, entomologists intent on capturing beetles, either pursued them with nets, turned over stones and logs, removed bark from trees, used beating trays or even dug holes in the ground, but never used pitfall traps! So all very active and energetic methods – no sit and wait in those days 😉 So it seems that Barber’s 1931 description of a pitfall trap does indeed commemorate the first scientific use of a pitfall trap.

The Barber trap (Barber, 1931).

Despite their late addition to the entomological armoury and despite the many criticisms levelled at their use, they continue to be perhaps the most widely used method of insect sampling ever; for example if you enter Beetle* AND pitfall* AND trap* into the Web of Science you will return 1168 hits since 2000, which is more than one a week. If you further refine your search to exclude beetle but add insect* you can add another 320 hits. If by some chance you have never used a pitfall trap, then I heartily recommend that you set one or two up in a convenient flower bed or even your lawn, and then sit back and wait and see what exciting beasties are roaming your garden.

Post script

Since this post was published I have discovered an earlier reference to the use of pitfall traps (Hertz, 1927). Many thanks to Jari Niemelä of Helsinki University for sending me a copy of the reference and many thanks to my eldest daughter for translating the relevant bit, which follows – “The traps were made of meticulously cleaned tin cans (the rectangle ones used for e.g. sardines) dug into the ground so deep that the top of the tin was absolutely level with the ground…… it is an ideal way to catch the beetles; with their careless way of running around, they easily fell into the deathtraps, and had no time to use their wings (if they have any)”. The phrase deathtraps is particularly fine. The majority of the paper is about the species he caught in different locations and he highlights the fact that he caught seven very rare species using this method.

So this is now the oldest known reference to the use of pitfall traps in the literature, although he does mention that he was using this method to catch beetles in 1914. But if anyone comes across an earlier reference do let me know.

I am always struck when reading the old entomological and ecological literature by how much the style of our writing has changed over the last 100 years or so, and not necessarily for the better 😉 I am not advocating a return to the writing style of the Victorian 3-volume novel but do think that we might try to be a bit less dry when reporting our science in mainstream journals. With the establishment of on-line publishing perhaps there will be less emphasis on word limits from Editors and publishers, but then on the other hand, we are all busy people and the number of papers published seems to be increasing at an exponential rate.

Here for your edification is a title from the mid-Victorian period; penned by John Curtis an English entomologist

Curtis, J. (1845) Observations on the natural history and economy of various insects etc., affecting the corn-crops, including the parasitic enemies of the wheat midge, the thrips, wheat louse, wheat bug and also the little worm called Vibrio. Journal of the Royal Agricultural Society, 6, 493-518.

John Curtis 1791-1862 (Photograph from Wikipedia)

There are also some great sentences in this paper that give you an insight into the character of the man and the conditions under which he worked, which we do not get in modern papers.

“I had hoped, during the past summer, to make some progress in the further development of the economy of the Wheat-midge; but although the little orange larvae were abundant in some wheat-fields in August in this neighbourhood, owing to the wet and cold season I presume, I did not discover a single midge on the wing, and the larvae appear to have all died as usual”

Later on writing about aphids; I couldn’t possibly not mention aphids 😉

“The corn-crops do not escape the visitations of this extensive tribe: indeed, what crop does?”

And from that great entomologist A R Wallace writing in 1865 on species distribution, Wallace, A.R. (1855) On the law which has regulated the introduction of new species. Journal of Natural History, 16, 184-196.

“Fully to enter into such a subject would occupy much space, and it is only in consequence of some views having been lately promulgated, he believes in a wrong direction, that he now ventures to present his ideas to the public, with only such obvious illustrations of the arguments and results as occur to him in a place far removed from all means of reference and exact information”

Obviously a man of great probity and conviction.

We all know of Darwin’s story, (Darwin, 1929), about having to put a beetle into his mouth having gone collecting beetles without suitable containers but how many of us know about this side of his character, also from the same source,

“A novel, according to my taste, does not come into the first class unless it contains some person whom one can thoroughly love, and if a pretty woman all the better”

“To the writer a potato plant has a characteristic smell, although not as strong as those from some other plants. When enclosed in the plant chamber, its odors are perhaps emanated along with the water vapour, which judged from the condensed portion, was considerable.”

And here in a relatively modern paper, from that intrepid entomologist Philip Darlington, P.J. (1970) Carabidae on tropical islands, especially the West Indies. Biotropica, 2, 7-15

“Mr Hlvac’s (1969) paper should be consulted for further details and discussion. But a very great deal still remains to be done on Scarites in Puerto Rico. Here obviously is another opportunity for exciting ecologic work, to be done under exceptional circumstances of comfort and convenience”

Non-entomologists will no doubt be familiar with Darlington from his classic species-area work on Caribbean herpetofauna.

So dear readers, which are your favourite memorable sentences and titles from the scientific literature? Please let me know.

I write about politics, nature + the environment. Some posts are serious, some not. These are my views, I don't do any promotional stuff and these views are not being expressed for anyone who employs me.

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